A tire withstands the weight of an automobile, reduces impact from the road, and transfers driving force or braking force of an automobile to the ground.
In general, a tire is a complex of fiber/steel/rubber, and has a structure as shown in FIG. 1.
Tread (1): a part contacting the road. It should afford frictional force required for driving, have good wear resistance, withstand external impact, and have low heat production.
Body ply, or carcass (6): a cord layer in the tire. It should support the vehicle weight, withstand impact, and have high fatigue resistance to bending and stretching while running.
Belt (5): located between the body plies, consists of steel wire in most cases, reduces external impact, and maintains a wide tread to afford excellent vehicle running stability.
Side wall (3): a rubber layer between a part below a shoulder (2) and bead (9). It protects the inner body ply (6).
Inner liner (7): located inside the tire instead of a tube, and prevents air leakage to enable a pneumatic tire.
Bead (9): square or hexagonal wire bundle formed of rubber-coated steel wire. It positions and fixes the tire to a rim.
Cap ply (4): a special cord located on a belt of a radial tire for some cars. It minimizes movement of the belt during running.
Apex (8): triangular rubber filler used to minimize dispersion of the bead, reduce external impact to protect the bead, and prevent air inflow during forming.
A tubeless tire where high pressure air of 30 to 40 psi is injected is commonly used without using a tube, and to prevent air leakage during automobile running, an inner liner having a high gas barrier property is positioned as the inner layer of the carcass.
Previously, a tire inner liner including rubber such as butyl rubber, halobutyl rubber, and the like having relatively low air permeability as a main ingredient was used, but to achieve a sufficient gas barrier property of the inner liner, the rubber content or inner liner thickness should be increased.
As the content and thickness of the rubber ingredient are increased, total weight of a tire is increased and the mileage of automobiles is reduced, and during vulcanization of a tire or running of automobiles, air pockets are generated between the inner rubber of a carcass layer and an inner liner, or the shape or properties of an inner liner is changed.
Therefore, various methods have been suggested to decrease the thickness and weight of the inner liner to increase mileage, to reduce changes in the shape or properties of the inner liner during vulcanization of a tire or running, and the like.
However, previously known methods have limitations in maintaining excellent air permeability and formability of a tire while sufficiently decreasing the thickness and weight of the inner liner.
In addition, the inner liner obtained by the previously known method often generated cracks due to repeated deformations during a manufacturing process of a tire or running of automobiles, and thus it did not have sufficient fatigue resistance.
Further, the previous tire inner liner did not have good adhesion to a carcass layer inside of a tire, and thus it was often separated or peeled off during a tire manufacturing process or running of automobiles.
Furthermore, the previous tire inner liner did not have a uniform thickness, and thus each part of the inner liner was non-uniformly deformed or elongated during a forming process.
Thus, mechanical properties of a tire inner liner were lowered, and during a tire manufacturing process or an automobile running process, a relatively largely elongated and thinned part was broken, and thus it was difficult to obtain a product having durability required for a tire.